The present invention relates generally to medical devices. More specifically, the present invention relates to catheters having improved proximal shaft designs. In particular, the invention includes kink-resistant proximal shafts, proximal shafts having less spring, and shafts having distally increasing flexibility.
Angioplasty procedures have gained wide acceptance in recent years as efficient and effective methods for treating types of vascular disease. In particular, angioplasty is widely used for opening stenoses in the coronary arteries and is used for treating stenoses in other vascular regions.
One widely used form of angioplasty makes use of a dilatation catheter which has a inflatable balloon at the distal end and a guide wire lumen within at least a portion of the catheter shaft. Typically, a guide wire is inserted through the vascular system to a position near the stenoses, leaving a proximal portion of the guide wire extending from the patient. The proximal guide wire portion is threaded through the dilatation catheter guide wire lumen and the dilatation catheter advanced through the vascular system over the guide wire to the position near the stenoses. The treating physician manipulates the dilatation catheter until the balloon is positioned across the stenoses. The balloon is then inflated by supplying fluid under pressure through an inflation lumen in the catheter to the balloon. The inflation of the balloon widens the lumen through the stenosed area by pressing the inflating balloon wall against the lesion inside wall.
Current angioplasty catheters often have a short strain relief surrounding a hypotube segment that forms the proximal shaft of the catheter. Hypotube, or thin-walled hypodermic tubing, has many desirable characteristics, but can kink if bent too sharply. Strain reliefs are commonly formed of a polymeric material extending distally from a manifold affixed to the proximal end of a catheter shaft. The current designs can inhibit kinking where the hypotube exits the manifold within the strain relief. Existing strain reliefs commonly have a length of about 1 to 2 inches. Some catheters are returned by users, having kinked proximal shaft regions in spite of the existing strain reliefs. Applicants believe catheter proximal shaft designs could be improved to further reduce kinking.
Catheters have flexibility requirements that vary with the location along the catheter length. Less flexibility may be required in the catheter proximal portion, where the catheter may lie within a large inside diameter, straight vessel portion. Greater flexibility is often a design goal in the catheter distal portion, where traversing small inside diameter, tortuous vessels may be required. In the catheter mid-region, a gradually, distally increasing flexibility is desirable rather than an abrupt change from low to high flexibility. What would be desirable is a catheter including a mid-region having a distally increasing flexibility while retaining the advantages of hypotube.
Present catheters having hypotube proximal shafts have the advantages of hypotube and one disadvantage of hypotube, that of sometimes excessive springiness. In use, current catheters can exhibit a large amount of spring or whipping about of the unconstrained portion. This can make handling the catheter somewhat difficult in the operating room. What would be desirable is a catheter having the advantages of a proximal hypotube portion but without the spring of current hypotube shafts.
The present invention includes catheters and subassemblies for catheters having improved proximal regions, and mid-regions including hypotube having distally increasing flexibility. One catheter has a kink-resistant proximal shaft including an outer tube disposed over a braid disposed over an inner tube, while not including hypotube in the proximal shaft. One catheter includes a kink-resistant proximal shaft having a 12-inch long strain relief disposed about a hypotube tubular region. Another catheter includes a proximal hypotube shaft having a set curve imparted through bending and annealing, resulting in a catheter hypotube shaft having reduced spring and decreased kink radius. One catheter subassembly includes a hypotube shaft having a cut in the hypotube wall to increase flexibility over the length of the shaft.
Some catheters, according to the present invention, have a braided polymeric proximal shaft in place of a hypotube proximal shaft and provide improved resistance to kinks, which can occur more often than desired in the proximal most 12 inches of catheter. One catheter has a polyethylene inner tube, a stainless steel wire braid over the inner tube, and a polyether block amide (PEBA) tube disposed over the braid. Some catheters, according to the present invention, include a proximal hypotube shaft having a long strain relief disposed over the hypotube to improve the kink resistance. One catheter has a strain relief about 12 inches long disposed over the proximal hypotube portion.
An improved catheter subassembly is provided by the present invention by setting a curve into hypotube for use in a catheter. One method includes wrapping a hypotube into a substantially circular shape, constraining the hypotube into that shape, annealing the hypotube, and releasing the hypotube. The resulting hypotube can have a slight curve imparted to the hypotube. The slight curve improves kink resistance and reduces the spring of the hypotube, while retaining the pushability.
A method for imparting increasing flexibility to a hypotube shaft is provided by the present invention. A hypotube region can have a spiral or helical cut made into the hypotube wall. In one method, the spiral cut extends through the wall. The flexibility of the hypotube can increase with increasing length over the spiral cut. One catheter including the spiral cut hypotube includes a polymeric sleeve disposed over the spiral cut so as to contain fluid within the lumen of the hypotube. One helical cut has decreasing inter-strand distance over the length of the cut, increasing flexibility over the length of the cut.